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Reverse engineering the human mind 177

Figure 10.3. d’Arsonval and colleagues showing the apparatus used to induce
visual phosphenes. This photo was taken in 1911.

duced movements of the hands without causing the subjects any discom-
fort. The magnetic pulse was generated by current (up to 8000A) flowing
through a small coil held above the subject’s head. The current is dis-
charged over a period of 1ms, reaching its peak in as little as 200 s and this
produces an intense magnetic pulse (approx. 2T) which in turn induces
current flow in the underlying cortical tissue. The techniques is painless
and safe as long as ethical and safety guidelines are followed.
The clinical neuroscience community was quick to pick up on the
importance of this discovery and Barker’s Transcranial Magnetic
Stimulation (TMS) was soon widely used to measure nerve conduction
velocities in clinical and surgical settings. However, it is not in the clini-
cal domain that magnetic stimulation provides the most excitement; mag-
netic stimulation is a tool with which to discover new facts about brain
function and it has already delivered in many areas.
I noted above that two of the problems with the lesion technique in
patients and non-human primates were that the process could not be
reversed and information about time was lost. With magnetic stimulation,